The bill of lading is the key document in sea freight: a receipt for the goods, evidence of the transport contract and, as an original, a document of title. Whoever holds the original can claim the cargo.
Common forms: original B/L (usually a set of 3), telex release (originals surrendered at origin, cargo released electronically) and sea waybill (no original, released to the named consignee).
As with air freight, there is a master B/L from the shipping line and a house B/L from the forwarder.